The London, Edinburgh and Dublin philosophical magazine and journal of science . wo from the base of the negativeleg of the carbon, it was brought down almost immediatelyto the potential of the negative terminal of the lamp. If themiddle plate is placed at a little distance from the carbonloop then, on testing by the condenser method, it is foundthat the plate is not instantly brought down to the potentialof the negative terminal, but that some few seconds have toelapse before this is the case. § 11. A series of experiments was then undertaken in orderto determine the effect of varying (1) the
The London, Edinburgh and Dublin philosophical magazine and journal of science . wo from the base of the negativeleg of the carbon, it was brought down almost immediatelyto the potential of the negative terminal of the lamp. If themiddle plate is placed at a little distance from the carbonloop then, on testing by the condenser method, it is foundthat the plate is not instantly brought down to the potentialof the negative terminal, but that some few seconds have toelapse before this is the case. § 11. A series of experiments was then undertaken in orderto determine the effect of varying (1) the surface, and (2) theposition of the metal plate in the bulb, and in these experi-ments the plate was sometimes of platinum and sometimes ofaluminium. In all cases the vacuum was a very perfect one,any occluded gases in the plates being got rid of by specialmeans. Edison Effect in Glow Lamps. 73 Experiment 8.—A normal 100-volt carbon-filament lamp,having a carbon filament coiled in a spiral of two turns (seefig. 7) bad a short stout platinum wire (*024 inch diain.) Fig. sealed across the bulb so as to thread through, withouttouching, the spirals of the carbon. The lamp at 100 voltstook 1*54 amperes and gave an illumination of 40 candles,equivalent to a power absorption of 3*9 watts per vacuum was very good. This lamp will hereafter becalled Lamp No. 1. As before, no current could be detectedby a galvanometer when joined up between the platinum wireand the negative electrode, but when the galvanometer wasconnected between the platinum wire and the positive elec-trode of the lamp a current of some milliamperes was foundpassing through it. As in the case of lamp No. 4, this lampwas characterized by a great tendency to change suddenlythe value of the current flowing through the galvanometerwhen the working volts on the lamp were kept perfectly con-stant. In the first series of observations the milamperemeterwas employed to measure the current flowing between
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